The present invention relates to a transmission system in which a bus-type or a loop-type transmission line is shared among plural communication apparatuses and data transmission is performed by using isochronous communication channels with bandwidths ensured. The present invention also relates to a bandwidth (resource) management apparatus and a bandwidth (resource) management method which are used in the transmission system, for managing resources such as the bandwidths or time slots for the transmission system.
As a conventional resource management method, there is a method used by a bus-type network according to an IEEE(Institute of Electrical and Electronics Engineers) 1394 High Performance Serial Bus (IEEE 1394) standard. As for the IEEE1394, articles as well as standard textbooks have been published, for example, Japanese articles appearing in the Interface(published in Japan) 1996, April, or the Interface 1997, (published in Japan) January.
FIG. 9 shows a transmission system which realizes the conventional resource management method. In FIG. 9, 81 denotes a resource management table, 82-1, 82-2, and 82-3 denote communication apparatuses, and 31 denotes a transmission line.
The communication apparatuses 82-1, 82-2, and 82-3 use an isochronous communication channel which ensures bandwidths or an asynchronous communication channel which does not ensure the bandwidths, to transmit data. Each of these communication apparatuses can freely determine which of the isochronous communication channel and the asynchronous communication channel is to be used by itself. In general, the isochronous communication channel is used to transmit data of a large capacity which requires isochronous transmission, such as video data or audio data, while the asynchronous communication channel is used to transmit data of a small capacity which does not require isochronous transmission, such as command or file transfer.
There is one resource management table 81 on the transmission line 31, which contains contents of allocation of network resources as the isochronous communication channels. The contents of resource allocation stored in the resource management table 81 can be overwritten for each of the communication apparatuses by communication using the asynchronous communication channel. The resource management table 81 contains the sum total of free bandwidths which are available as the isochronous communication channels, that is, which are not allocated to any communication apparatuses, BANDWIDTH_AVAILABLE (BW_A). The communication apparatus 82-1, before starting data transmission using the isochronous communication channel, obtains a bandwidth to-be-ensured from BW_A as a resource to-be-ensured, and performs data transmission by using the ensured bandwidth. In this case, if the resource to-be-ensured exceeds the BW_A, the apparatus 82-1 cannot be ensured the bandwidth. When data transmission is completed and the resource is released, the released bandwidth is added to the BW_A. The above operation enables to allocate the bandwidth required for the communication apparatus 82-1.
FIG. 10 schematically shows a data transmission format according to IEEE1394. In FIG. 10, reference numerals 91, 92, and 93 denote a cycle start, an isochronous packet, and an asynchronous packet, respectively. The format shown in FIG. 10 illustrates a transmission format of one cycle as a basic unit for IEEE1394 transmission. This cycle is repeated to implement data transmission. One cycle is 125 micro seconds starting from the cycle start 91. The isochronous packet 92 which implements data transmission using the isochronous channel and the asynchronous packet 93 which implements transmission using the asynchronous communication channel are used as packets to-be-transmitted. The maximum length of the isochronous packet which can be transmitted by the communication apparatus in each cycle is assumed to be an arbitrary length below a value determined by the ensured bandwidth which is obtained from the resource management table 81. Thereby, respective communication apparatuses can share the transmission line by using set respective bandwidths.
Hence, according to the conventional transmission system, the bandwidth ensured in advance by each of the communication apparatuses is ensured until the end of communication with no change made. This is suitable for data transmission which requires that a constant bandwidth be always ensured. Such data is defined as CBR (constant bit rate) data. On the other hand, when transmitting a file or map data of a large capacity, isochronous transmission is not required but bandwidths needs to be ensured because of its large capacity, and therefore the isochronous communication channel is used to perform data transmission. Such non-isochronous data of a large capacity is defined as ABR (available bit rate)data. The ABR data has a request relating to the maximum bandwidth and the minimum bandwidth, and demands to ensure an arbitrary bandwidth between the maximum bandwidth and the minimum bandwidth. When transmitting the ABR data, a data rate of the data to-be-transmitted can be changed according to the ensured bandwidth. However, when transmitting the ABR data by using the isochronous communication channel in the conventional transmission system, a bandwidth which was initially ensured is used to perform data transmission. As a consequence, the bandwidth cannot be allocated flexibly.
The present invention is directed to solving the above problem, and an object of the present invention is to provide a transmission system which is capable of allocating resources more flexibly.
Other objects and advantages of the invention will become apparent from the detailed description that follows. The detailed description and specific embodiments described are provided only for illustration since various additions and modifications within the spirit of and scope of the invention will be apparent to those skill in the art from the detailed description.
According to a first aspect of the present invention, there is provided a transmission system comprising a transmission line, a communication apparatus connected to the transmission line, and a bandwidth management apparatus for managing bandwidths on the transmission line, wherein the communication apparatus, when performing isochronous data transmission by using an allocated resource on the transmission line, outputs a resource allocation request including information indicating a minimum bandwidth and a maximum bandwidth to the bandwidth management apparatus before the isochronous data transmission, and wherein the bandwidth management apparatus includes an allocated-resource request table for storing plural allocated-resource requests; and resource management means which decides whether or not sum of minimum bandwidths of all allocated-resource requests stored in the allocated-resource request table and a minimum bandwidth of the resource allocation request is allocatable from resources on the transmission line when receiving the resource allocation request as an input, allocates a resource for each of the all allocated-resource requests and the resource allocation request such that a bandwidth between a corresponding minimum bandwidth and a corresponding maximum bandwidth is allocated when deciding that the sum is allocatable, and writes the minimum bandwidth and an allocated bandwidth of the resource allocation request in the allocated-resource request table as an allocated-resource request. Therefore, when making the resource allocation request, resource allocation for the request is performed with higher probability.
According to a second aspect of the present invention, in the transmission system of the first aspect, the resource management means, when an allocated resource of at least one allocated-resource request stored in the allocated-resource request table is released, reallocates a free resource for each of allocated-resource requests other than the at least one allocated-resource request with the allocated resource released such that a bandwidth which is not larger than a corresponding maximum bandwidth is obtained. Therefore, the resource can be utilized effectively.
According to a third aspect of the present invention, in the transmission system of the first aspect, the resource management means, when allocating the resource such that the bandwidth between the corresponding minimum bandwidth and the corresponding maximum bandwidth is allocated, performs control so that a ratio of an allocated bandwidth to a corresponding maximum bandwidth for a first request of a priority is higher than a ratio of an allocated bandwidth to a corresponding maximum bandwidth for a second request of a priority lower than the priority of the first request. Therefore, a larger bandwidth is allocated for a request of a higher priority.
According to a fourth aspect of the present invention, there is provided a transmission system comprising a transmission line, plural communication apparatuses connected to the transmission line, and a bandwidth management apparatus for managing bandwidths on the transmission line, wherein a communication apparatus included in the plural communication apparatuses, when performing isochronous data transmission by using an allocated resource on the transmission line, outputs a resource allocation request to the bandwidth management apparatus before the isochronous data transmission, and outputs the resource allocation request again upon receipt of free resource increase notification, when negative acknowledgement is sent to the communication apparatus in response to the resource allocation request, and wherein the bandwidth management apparatus manages resources on the transmission line, sends the negative acknowledgement to the communication apparatus when resource allocation for the resource allocation request from the communication apparatus is impossible, and notifies all the communication apparatuses that free resources are increased, by broadcast, when an allocated resource is released. Therefore, for the communication apparatus whose request has been once rejected, the resource can be allocated later.
According to a fifth aspect of the present invention, there is provided a transmission system comprising a transmission line, plural communication apparatuses connected to the transmission line, and a bandwidth management apparatus for managing bandwidths on the transmission line, wherein a communication apparatus included in the plural communication apparatuses, when performing data transmission by using an allocated resource on the transmission line, outputs a resource allocation request including a priority to the bandwidth management apparatus before the data transmission, and wherein the bandwidth management apparatus manages resources on the transmission line in such a way that it releases resources allocated for another communication apparatuses and allocates the resources for the resource allocation request, when resource allocation for the resource allocation request from the communication apparatus is impossible and the priority of the resource allocation request is the highest. Therefore, for data transmission with higher urgency, the resource allocation is always performed.
According to a sixth aspect of the present invention, there is provided a transmission system comprising a transmission line, at least two communication apparatuses connected to the transmission line, and a bandwidth management apparatus for managing bandwidths on the transmission line, the transmission line being divided into time slots at regular intervals, wherein each of the at least two communication apparatuses, includes resource request means which outputs a resource allocation request to the bandwidth management apparatus before isochronous data transmission, for performing the isochronous data transmission by using an allocated resource on the transmission line; and delay means which stores data input externally and then outputs the data toward the transmission line, for transmitting the data toward the transmission line, and stores data received through the transmission line and then outputs the data externally, for receiving the data through the transmission line, and wherein the bandwidth management apparatus receives the resource allocation request, and when allocating a resource for the resource allocation request, verifies that the delay means of the communication apparatus will not overflow when the resource is allocated. Therefore, variances of data arrival times due to data transmission can be compensated for with fewer memories.
According to a seventh aspect of the present invention, there is provided a bandwidth management apparatus for managing resources on a transmission line and processing a resource allocation request including information indicating a minimum bandwidth and a maximum bandwidth, which comprises: an allocated-resource request table for storing plural allocated-resource requests; and resource management means which decides whether or not sum of minimum bandwidths of all allocated-resource requests stored in the allocated-resource request table and a minimum bandwidth of the resource allocation request is allocatable from the resources on the transmission line when receiving the resource allocation request as an input, allocates a resource for each of the allocated-resource requests and the resource allocation request such that a bandwidth between a corresponding minimum bandwidth and a corresponding maximum bandwidth is allocated when deciding that the sum is allocatable, and writes the minimum bandwidth and an allocated bandwidth of the resource allocation request in the allocated-resource request table as an allocated-resource request. Therefore, when making the resource allocation request, resource allocation for the request is performed with higher probability.
According to an eighth aspect of the present invention, there is provided a bandwidth management apparatus for managing resources on a transmission line and processing a resource allocation request, which comprises: means for broadcasting free resource increase notification through the transmission line when an allocated resource is released. Therefore, for the communication apparatus whose request has been once rejected, the resource can be allocated later.
According to a ninth aspect of the present invention, there is provided a bandwidth management apparatus for managing resources on a transmission line and processing a resource allocation request including a priority, which comprises: means which releases an allocated resource when resource allocation for the resource allocation request is impossible and the priority of the resource allocation is the highest, and performs resource allocation for the resource allocation request. Therefore, for data transmission with higher urgency, the resource allocation is always performed.
According to a tenth aspect of the present invention, there is provided a bandwidth management apparatus which is applied to a transmission system comprising a transmission line, and at least two communication apparatuses connected to the transmission line which is divided into time slots at regular intervals, for managing allocation of the time slots and processing a resource allocation request, which comprises: means which verifies that delay means for delaying data in a communication apparatus of the at least two communication apparatuses will not overflow, when it allocates the time slots for the resource allocation request and the communication apparatus transmits data by using the time slots allocated for itself. Therefore, variances of data arrival times due to data transmission can be compensated for with fewer memories.
According to an eleventh aspect of the present invention, there is provided a bandwidth management method for managing resources on a transmission line by using an allocated-resource request table for storing plural allocated-resource requests, which comprises: deciding whether or not sum of minimum bandwidths of all allocated-resource requests stored in the allocated-resource request table and a minimum bandwidth of the resource allocation request is allocatable from the resources on the transmission line when receiving the resource allocation request as an input; and allocating a resource for each of the all allocated-resource requests and the resource allocation request such that a bandwidth between a corresponding minimum bandwidth and a corresponding maximum bandwidth is allocated when deciding that the sum is allocatable, and writing the minimum bandwidth and an allocated bandwidth of the resource allocation request in the allocated-resource request table as an allocated-resource request. Therefore, when making the resource allocation request, resource allocation for the request is performed with higher probability.
According to a twelfth aspect of the present invention, there is provided a bandwidth management method for managing resources on a transmission line to which plural communication apparatuses are connected, wherein when an allocated resource is released, all of the plural communication apparatuses are notified that free resources are increased, by broadcast. Therefore, for the communication apparatus whose request has been once rejected, the resource can be allocated later.
According to a thirteenth aspect of the present invention, there is provided a bandwidth management method for managing resources on a transmission line, which comprises: an allocation decision step for deciding whether or not a resource is allocatable for a resource allocation request when receiving the resource allocation request including a priority as an input; a priority decision step for deciding whether or not the priority of the resource allocation request is not smaller than a predetermined value when it is decided that the resource is not allocatable for the resource allocation request in the allocation decision step; and a release step for releasing an allocated resource when the priority is not smaller than the predetermined value, and returning to the allocation decision step. Therefore, for data transmission with higher urgency, the resource allocation is always performed.
According to a fourteenth aspect of the present invention, there is provided a band management method which is applied to a transmission system comprising a transmission line and at least two communication apparatuses, the at least two communication apparatuses each including delay means for delaying data and the transmission line being divided into time slots at regular intervals, and which is used for managing the time slots, and the method comprises: a step for verifying that the delay means of a communication apparatus which will transmit data, included in the at least two communication apparatuses, will not overflow, when the time slots are allocated for a resource allocation request received as an input, and the communication apparatus transmits data by using the time slots allocated for itself. Therefore, variances of data arrival times due to data transmission can be compensated for with fewer memories.